Catalytic cracking of naphtha and gas oil

ABSTRACT

Low octane naphtha and fresh gas oil are catalytically cracked with a zeolite catalytic cracking catalyst in separate elongated reaction zones yielding a naphtha having an increased octane rating. Recovering a naphtha fraction, particularly a heavy naphtha fraction, from the cracked product, and combining it with the fresh naphtha feed, further enhances the octane rating of the naphtha product. A cycle gas oil may be recovered from the reactor effluent and combined with the fresh naphtha feed or introduced into a separate (a third) elongated reaction zone to effect maximum recovery of naphtha and lighter stocks having improved product quality. Optionally, any of the feedstocks may be subjected to further cracking in a dense bed of the zeolite catalyst.

United States Patent [191 Reynolds et al.

[451 Jan. 8, 1974 1 CATALYTIC CRACKING OF NAPI-ITI'IA AND GAS OIL [75]Inventors: David L. Reynolds, Nederland;

Douglas J. Youngblood, Groves; Dorrance P. Bunn, Jr., Houston; Roy E.Pratt, Groves, all of Tex.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Oct. 2, 1970 [21] Appl. No.: 77,479

[52] U.S. Cl. 208/74, 208/DIG. 2, 208/77, 208/120, 208/164 [51] Int. ClCl0g 11/18, C10g 37/02, B01j 9/20 [58] Field of Search 208/74, 78

[56] References Cited UNITED STATES PATENTS 2,409,353 10/1946 Giulianiet a1. 208/120 3,649,522 3/1972 Martin 208/120 3,692,667 9/1972 McKinneyet a1. 208/120 3,679,576 7/1972 McDonald 208/74 3,143,491 8/1964Bergstrom.... 208/74 3,424,672 1/1969 Mitchell 208/164 3,065,166 11/1962Hennig ..'208/67 2,890,164 6/1962 Woertz 208/74 Primary Examiner-DelbertE. Gantz Assistant Examiner-G. E. Schmit'kons Attorney-Thomas H. Whaleyand Carl G. Reis 5 7 ABSTRACT Low octane naphtha and fresh gas oil arecatalytically cracked with a zeolite catalytic cracking catalyst inseparate elongated reaction zones yielding a naphtha having an increasedoctane rating. Recovering a naphtha fraction, particularly a heavynaphtha fraction, from the cracked product, and combining it with thefresh naphtha feed, further enhances the octane rating of the naphthaproduct. A cycle gas oil may be recovered from the reactor effluent andcombined with the fresh naphtha feed or introduced into a separate (athird) elongated reaction zone to effect maximum recovery of naphthaandlighter stocks having improved product quality. Optionally, any of thefeedstocks may be subjected to further cracking in a dense bed of thezeolite catalyst.

29 Claims, 2 Drawing Figures CATALYTIC CRACKING OF NAPIITI'IA AND GASOIL CROSS-REFERENCE TO RELATED APPLICATIONS This is related toapplication Ser. No. 77,480 which discloses the fluid catalyticcracking, in risers, of low octane naphtha and a recycle stream of fullrange naphtha or heavy naphtha and application Ser, No. 889,714 whichdiscloses the catalytic cracking of naphtha with crystallinealuminosilicate catalyst.

BACKGROUND OF THE INVENTION This invention relates to the catalyticcracking of hydrocarbons. In particular this invention relates to thefluid catalytic cracking of fresh gas oil and naphtha having a lowoctane rating and boiling in the range of IO450F.

Gasoline is frequently blended from stocks, including naphtha, theoctane of which has been increased through catalytic reforming. Bothvirgin and cracked stocks may be upgraded by reforming operations.Catalytic reformers are usually operated to provide the desired octaneimprovement with the least conversion of gasoline to saturated butanesand lighter materials.

The gasoline blending pool is maintained by a variety of operationsisobutanes and butenes, for example, are charged to alkylation units andlight olefins are polymerized to provide high octane blending componentswhile the catalytic cracking of gas oil augments the supply of naphthaas well as providing additional feed for alkylation and polymerizationunits. Although hydrocracking provides additional quantities of gasolineblending naphthas, the heavy naphtha from hydrocracking often has arelatively low octane number.

Recently the introduction of zeolite cracking catalysts has effectedsignificant improvements in the catalytic cracking operation. Whenemployed for gas oil cracking in existing catalytic cracking units thesehighly active catalysts have produced increased throughput and improvedproduct quality. In addition, catalytic cracking apparatus, such asdisclosed in U.S. Pat. Nos. 3,433,733 and 3,448,037, has been developedspecifically for use with these improved catalysts. This apparatusincorporates the concept of riser cracking wherein the feedstocks arecracked in elongated reaction zones or risers terminating in a taperedreactor containing a dense phase and dilute phase of catalyst. A mixtureof zeolite catalyst and gas oil passes through the riser under crackingconditions which are tailored to the particular feedstock and desiredproducts. After passing through the riser further cracking of the feedcan be achieved, if necessary, in the fluidized dense phase of catalystin the reactor.

Although the zeolite catalysts increase the supply of high qualitynaphtha, yields of the lighter hydrocarbons are substantially lower thanfrom catalytic cracking with amorphous silica-alumina catalysts. In thefuture, therefore, the supply of isobutane, propylene and butene foralkylate production and of these and other light hydrocarbons forpolymerization and petrochemical manufacture will continually decline. Aprocess which will upgrade naphtha streams for use in gasoline blendingand supply additional quantities of C4 and lighter hydrocarbons ishighly desirable.

Naphtha is more difficult to crack than gas oil and up to the presenttime limited success has been obtained in cracking naphthacatalytically. Traditional cracking catalyst, such as silica-alumina,exhibited relatively poor selectivity and activity when employed tocrack naphtha resulting in the formation of relatively large amounts ofgas and coke and producing small amounts of desirable olefins andaromatics. U.S. Pat. No. 3,284,341 discloses a process for the catalyticcracking of naphtha with a silica-alumina. catalyst to producesubstantial quantities of olefins and aromatics by maintaining the spacevelocity above about 4.5, the pressure between 0 and 20 psig and thereaction temperature between 1,000 and 1,200F.

The new zeolite cracking catalysts are being employed extensively in gasoil cracking operations but their utility for the conversion of naphthahas yet to be fully explored. U.S. Pat. No. 3,247,098 discloses thathydrogen mordenite, a crystalline aluminosilicate, is an extremelyactive catalyst for the conversion of light naphtha to lightercomponents together with improving the octane number of the resultantnaphtha. The utility of the mordenite alumino-silicate as a crackingcatalyst for naphtha was found to be surprising in view of theineffectiveness of a magnesium faujasite catalyst to satisfactorilycrack naphtha. Magnesium faujasite was known to be a highly effectivegas oil cracking catalyst. The development of processes which mayusefully be employed for the cracking of naphtha and gas oil and whichwill be selective for the production of light hydrocarbons as well asnaphthas having enhanced octane ratings is highly desirable.

SUMMARY OF THE INVENTION Broadly, our invention is directed to thecatalytic cracking of gas oils boiling in the range of about430-l,050lF. and naphthas boiling in the range of about l0O450F. toproduce substantial quantities of naphtha having an octane ratingsignificantly higher than that of the low octane naphtha feed andyielding substantial quantities of lighter hydrocarbons which may serveas feed for alkylate and petrochemical manufacture. A fluid catalyticcracking unit having multiple risers and employing zeolite crackingcatalysts has been found to offer particular utility for the catalyticcracking of such feed streams. The naphtha and the gas oil arecatalytically cracked in separate cracking zones under conditionsspecifically tailored to the particular feedstock. In addition, a fullrange or heavy naphtha cut may be removed from the reactor effluent forrecycling to the fresh naphtha cracking zone and a cycle gas oil mayalso be removed from the reactor effluent for introduction into thefresh naphtha cracking zone or into a separate (third) cracking zone toeffect maximum recovery of naphtha and lighter stocks having improvedproduct quality. A cracking zone may be limited to an elongated reactionzone, also known as a riser, or a combination of an elongated reactionzone and the dense phase of catalyst in the reactor vessel.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be morereadily understood by reference to FIG. I which depicts a flow diagramof a preferred embodiment of the process of the invention and to FIG. 2which depicts an apparatus for carrying out a preferred embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Broadly, we have found that theoctane rating of a low octane naphtha can be significantly improved bycatalytically cracking it in a fluid catalytic cracking unit employing amultiplicity of elongated reaction zones, hereinafter called risers orriser conduits, wherein the low octane naphtha is introduced into one ofthe risers and fresh gas oil is introduced into a second riser.Operating conditions within the several risers are established to obtainoptimum product yield and product quality from each of the individualstreams. Broadly, our process contemplates a process for the catalyticcracking of naphtha and gas oil with a zeolite cracking catalyst in afluid catalytic cracking unit comprising a reactor, a regenerator and amultiplicity of elongated reaction zones wherein said reactor contains adense phase and a dilute phase of said catalyst and said elongatedreaction zones terminate at said reactor which comprises:

a. passing a naphtha stream and a zeolite cracking catalyst through afirst elongated reaction zone under naphtha cracking conditions,

b. passing a gas oil and a zeolite cracking catalyst through a secondelongated reaction Zone under gas oil cracking conditions,

, c. discharging the effluents from said first and second reaction zonesinto a catalyst phase in said reactor, said effluents comprisingvaporous reaction mixture and catalyst, and

d. recovering from the vaporous reaction mixture in a dilute phase ofcatalyst in said reactor a fraction boiling in the range of 100 to 450F.having an octane rating higher than said naphtha stream and a fractionboilingbelow 100F.

The catalyst phase into which the effluent from a particular riserdischarges may be either the dense phase or the dilute phase of catalystin the reactor which leads to a number of optional embodimentsincorporating various combinations of riser cracking and dense phasecracking, i.e., bed cracking.

In the simplest embodiment, the cracking of both naphtha and gas oil isrestricted to the risers by discharging the effluent from both risersinto the dilute phase of catalyst in the reactor vessel. In thissituation the reactor vessel is utilized as a disengaging zone withlittle or no cracking taking place therein.

In another embodiment, the gas oil is subjected to further cracking inthe dense catalyst phase. This is achieved by discharging the effluentfrom the naphtha riser into the dilute phase of catalyst and theeffluent from the gas oil riser into the dense phase of catalyst, thevaporous reaction mixture from the gas oil riser passes through thedense phase of catalyst under catalytic cracking conditions effecting anadditional conversion of 5 to 30 volume percent and discharges into thedilute phase of catalyst.

In a further embodiment, the gas oil is subjected only to riser crackingwhile the naphtha is cracked in both the riser and the dense phase ofcatalyst. The effluent from the gas oil riser is discharged directlyinto the dilute phase of catalyst in the reactor vessel while theeffluent from the naptha riser is discharged into the dense phase ofcatalyst, the vaporous reaction mixture from the naphtha riser passesthrough this dense phase under catalytic cracking conditions effectingan additional conversion of 5 to 30 volume percent and discharges intothe dilute phase of catalyst.

In another embodiment, the gas oil and the naphtha are both subjected toriser cracking and bed cracking by discharging the effluent from bothrisers into the dense phase of catalyst. The vaporous reaction mixturepasses through the dense phase under catalytic cracking conditions toeffect an additional conversion of each stream of 5 to 30 volume percentand discharges into the dilute phase.

In another series of embodiments a cycle gas oil is recovered from theeffluent from the catalytic cracking unit and recycled to the unitwherein it is subjected to riser cracking in a third elongated reactionzone and bed cracking in the dense phase of catalyst in the reactor.This embodiment envisions the following additional steps which may beoptionally added to any of the above four embodiments:

e. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling above about500F.,

f. passing said fraction of step (e) and a zeolite cracking catalystthrough a third elongated reaction zone under cycle gas oil crackingconditions, and

g. discharging the effluent from said third elongated reaction zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions effecting an additional conversionof 5-30 volume percent and discharging into a dilute phase of catalyst.

In still another series of embodiments cycle gas oil may be recoveredfrom the effluent from the catalytic cracking unit and recycled to thenaphtha riser where it is subjected, together with the naphtha, to bothriser and bed cracking. This will permit two more optional embodimentswherein the fresh gas oil is subjected to riser cracking only or acombination of riser and bed cracking.

Another group of optional embodiments envisions the use of a recyclenaphtha stream. A naphtha cut which may be either a full range naphtha,i.e., about a -450F. boiling range, or a heavy naphtha, i.e., about a250450F. boiling range, may be removed from the reactor effluent andrecycled for introduction into the naphtha riser wherein it is combinedwith the fresh naphtha and subjected to both riser and bed cracking.Fresh gas oil is introduced into a separate riser. In this two-riserconcept the fresh naphtha and the recycle naphtha are subjected to bothriser and bed cracking. With the fresh gas oil subjected either to risercracking only or riser and bed cracking, two more additional embodimentsare possible. The following additional steps relating to the naphtharecycle are added:

j. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling between 100 and450F., and

k. introducing the fraction from step (j) into the first elongatedreaction zone effecting conversion of said fraction.

Two more optional embodiments envision two recycle streams, cycle gasoil and recycle naphtha, and the use of three risers. Both recyclestreams are recovered from the reactor effluent as explained above indescribing other embodiments. In this three-riser concept the recyclenaphtha is combined with fresh naphtha and the combined streams arepassed through the naphtha riser and subjected to both riser and bedcracking. The cycle gas oil is introduced to its own riser and iscracked in both the riser and the bed of catalyst in the reactor. Thefresh gas oil passes through a third riser and is subjected to risercracking only in one embodiment or both riser and bed cracking in theother.

In accordance with this invention the fresh feedstocks for this processcomprise naphtha and gas oil. The naphtha feedstocks comprisehydrocarbons boiling in the range of about lOO-450F. and include manyrefinery streams having low economic value which may be upgraded throughthe process of our invention. Useful naphtha feedstocks are usuallyhighly paraffinic and include such light hydrocarbon fractions as lowoctane naphtha, aromatic solvent extraction raffinate, thermal crackednaphtha, coker naphtha, low octane naphtha from hydrocracking operationsand straight run naphthas. As used herein, the term low octane freshnaphtha refers to these useful feedstocks. Because of the refractoryquality of these naphtha feed streams, they must be subjected to moresevere conditions than is the fresh gas oil feed if significantconversion is to be obtained.

The gas oil feed in our process comprises petroleum stocks boiling fromabout 430 to 1,050F. and comprises heavy atmospheric gas oil, light andheavy vacuum gas oils, gas oil from coking operations, vis-broken gasoil, deasphalted gas oil, decarbonized gas oil, hydrotreated gas oil,hydrocracked gas oil and solvent extracted gas oil. All of thesefeedstocks are petroleum stocks whose processing has not previouslyincluded fluid catalytic cracking and are commonly referred to,therefore, as virgin gas oils.

Products from the process of our invention include naphthas withimproved octane ratings and hydrocarbons boiling below the initialboiling point of the naphtha feed which will find particular utility asfeed streams for petrochemical and gasoline manufacture.

The catalyst employed in the instant invention is a cracking catalyst ofthe zeolite type as exemplified by those catalysts wherein a crystallinealuminosilicate is dispersed in a siliceous matrix. Among the preferredzeolites which may be usefully employed in the catalyst used in theprocess of our invention are those known as zeolite X and zeolite Y,including both the naturally occurring and synthetic varieties. Becauseof their extremely high activity, these zeolite materials are compositedwith a material processing a substantially lower level of catalyticactivity, a siliceous matrix which may be of the synthetic,semi-synthetic or natural type. The materials may includesilica-alumina, silica-gel, silicaberyllia, silica-magnesia,silica-thoria or silica-zirconia which have been successfully employedheretofore. In general, the composite crystalline zeolite catalystcomprises about 1 to 50 weight percent zeolite, about 5 to 50 weightpercent alumina and the remainder silica. The crystallinealuminosilicate portion of the catalyst composition is a natural orsynthetic, alkali metal, crystalline aluminosilicate which has beentreated to replace all or at least a substantial portion of the originalalkali metal ions with other ions such as hydrogen and- /or a metal orcombination of metals such as barium, calcium, magnesium, manganese orrare earth metals, for example, cerium, lanthanum, neodymium,praseodymium, samarium and yttrium. The crystalline zeolitescontemplated above may be represented by the formula M21 0 1 A1203 I y HO where M represents hydrogen or a metal, n its valence, x has a valueranging from 2 to 10 and y ranges from 0 to Ml, in dehydrated zeolites ywill be substantially O. In the instant invention the preferredcrystalline zeolites are either natural or synthetic zeolite X orzeolite Y. In highly preferred embodiments m is selected from the groupconsisting of hydrogen, calcium, magnesium and the rare earth metals.

Those skilled in the art will readily appreciate that the catalyticcracking equipment currently employed in the petroleum industry whichincorporates the concept of riser cracking may be utilized to practicesome embodiments of our invention. A particularly preferred apparatus isthat described in U.S. Pat. No. 3,433,733 wherein the charge stocks arecracked in two elongated reaction zones or risers terminating in atapered reactor chamber wherein further dense bed cracking may takeplace. One riser passes through the tapered wall of the reactorterminating in a downwardly directed outlet while the second riserpasses through the bottom of the reactor discharging upwardly into thereactor. The cracking apparatus incorporates a stripping section beneath the dense fluid bed wherein entrained and adsorbed hydrocarbonsare displaced from the catalyst by means of steam as the catalyst passesfrom the reactor to the regeneration vessel. As with conventional fluidcatalytic cracking equipment, the catalyst is contacted with anoxygen-containing gas in the regenerator to effect combustion of atleast a portion of the deposited coke. The regenerated catalyst is thenreintroduced into the bottom of the risers at a point where thefeedstocks are introduced. By introducing fresh gas oil to one riser andcycle gas oil to the other, it is possible to operate the individualrisers under conditions specifically tailored to obtain the desiredcracking of the particular feedstock passing therethrough. The overalleffect, of course, is to achieve optimum performance of both the fluidcatalytic cracking; unit and the zeolitic cracking catalyst beingemployed.

Those embodiments of this invention requiring two risers may beconducted, for example, in the apparatus described in US. Pat. No.3,433,733 by D. P. Bunn,

Jr. et al. and discussed above. When the embodiment necessitates the useof three risers, an apparatus such as depicted in FIG. 2 may be employedwhich is an improvement over the apparatus of Bunn et al. Broadly, thisimproved embodiment may be described as follows: in an apparatus forfluid catalytic cracking of a type comprising:

a. a reactor chamber having a tapered portion of greater diameter at theupper portion than at the lower h. means to withdraw solids from thelower portion of the reactor chamber and to discharge the same into thestripping chamber,

i. means to introduce steam into the lower portion of the strippingchamber,

j. means to withdraw solids from the lower portion of the strippingchamber and to discharge the same into the regenerator chamber,

k. means to introduce combustion gas into the lower portion of theregenerator chamber,

' 1. means to withdraw flue gas from the upper portion of theregenerator chamber,

m. means to withdraw regenerated catalyst from the regenerator chamberand to discharge the same into the inlet of the riser conduits, and

n. means to introduce oil feed into the inlet of said riser conduits,the improvement which comprises:

1. a first riser conduit entering and passing through a wall of thereactor chamber and discharging into the reactor chamber,

2. a second riser conduit entering and passing through a wall of thereactor chamber and discharging into the reactor chamber at a pointabove the discharge point of the first riser, and

3. a third riser conduit entering and passing through a wall of thereactor chamber and discharging into the reactor chamber at a pointintermediate the discharge points of the first and second riser con-'duits.

In preferred embodiments, the first riser conduit may pass through thebottom wall of the reactor chamber, the second riser conduit through theside wall of the reactor chamber or the third riser conduit through theside wall of the reactor chamber. In other preferred embodiments, thefirst riser conduit may terminate in the reactor chamber in an upwardlydirected outlet, the second riser conduit in a downwardly directedoutlet or the third riser conduit in a downwardly directed outlet.

In the naphtha riser, the operating conditions contemplated hereininclude a temperature of 750-l ,300F., preferably 900-l ,000F., aconversion per pass of 25-80 volume percent, preferably 30-60 volumepercent, and a vapor velocity of 15-50 feet/- second, preferablyfeet/second. In the fresh gas oil riser, the operating conditionsinclude a temperature of 840-l,lO0F., preferably 890l,000F., aconversion per pass of 30-80 volume percent, preferably 40-65 volumepercent, and a vapor velocity of 15-50 feet/second, preferably 20-40feet/second. When cycle gas oil is introduced into a third riser theoperating conditions in this riser include a temperature of 800-l ,lF.,preferably 850-l,00OF., a conversion per pass of 20-70 volume percent,preferably 30-50 volume percent, and a vapor velocity of 15-50 feet/-second, preferably 20-40 feet/second. When cracking in the dense phaseof catalyst, i.e., bed cracking, is employed the operating conditions inthe bed include a temperature of 800-l,l50F., a conversion of -30 volumepercent and a vapor velocity of 0.5-4 feet/- second, preferably 1.3-2.2feet/second. When the term conversion is used herein in connection withvirgin gas oil or cycle gas oil a 430F conversion is intended and isdefined as 100 minus the volume percent of product boiling above 430F.When conversion is used herein in connection with naphtha or recyclenaphtha a 1 F conversion is intended and is defined as minus the volumepercent of product boiling above F.

The invention may be understood from the following detailed descriptiontaken with reference to FIG. 1 which illustrates and exemplifies a meansby which the process of the present invention may be practiced. Bydescribing our invention in this manner it is not intended to restrictthe invention thereby since modifications to the following descriptionmay be made within the scope of the claims without departing from thespirit thereof.

In this description a preferred embodiment incorporating three risers isemployed. A heavy naphtha recycle is combined with fresh naphtha andintroduced to one riser, fresh gas oil is fed to another riser and cyclegas oil to the third riser. The combined naphtha streams and the cyclegas oil are subjected to both riser and bed cracking while the fresh gasoil only undergoes riser cracking.

Fresh naphtha obtained from a variety of sources, not shown, passesthrough line 10 and is combined with a heavy naphtha stream passingthrough line 12. The heavy naphtha is a cracked stream and is recoveredfrom an effluent stream as described hereinafter. These combined streamsare introduced into riser 14 where they are brought into contact withhot regenerated zeolite cracking catalyst from standpipe 16. Theresulting suspension of catalyst-naphtha vapor passes up riser 14 intoreactor 18. The reactor contains a bed of catalyst 20 referred to as thedense phase of catalyst, and a vapor space 22 above the bed of catalystwhich functions as a catalyst disengaging space and is referred to asthe dilute phase of catalyst. The effluent from riser l4 discharges intothe lower portion of reactor 18 and passes upward through the densephase of catalytic cracking catalyst 20 effecting further conversion ofthe combined naphtha streams.

A fresh gas oil stream is introduced through line 24 to riser 26 whereit is contacted with regenerated zeolite cracking catalyst fromstandpipe 28. The resultant catalyst-in-gas oil vapor passes up riser 26to reactor 18 discharging into the dilute phase of catalyst 22 whereinthe catalyst particles disengage from the vaporous reaction mixture andfall into the bed of catalyst 20.

An intermediate gas oil stream, obtained from the effluent from thecatalytic cracking unit as described hereinafter, passes through line 30into riser 32 where it is contacted with hot regenerated zeolitecracking catalyst from standpipe 34. The resultant suspension ofcatalyst-in-cycle gas oil vapor passes up riser 32 into reactor 18discharging into the dense phase of catalyst 20. The vapor mixturepasses upwardly through the bed of catalyst effecting some furtherconversion of the cycle gas oil.

Cracked products disengage from the catalyst in the dilute phase ofcatalyst 22 above the catalyst dense phase 20. These vapors, togetherwith any entrained catalyst, pass through cyclone separators, not shown,wherein this catalyst is substantially separated from the vapors andreturned to the catalyst bed. Effluent gases containing the crackedproducts pass through line 36 to fractionator section 38 wherein thevapor mixture is separated into various products. These productsinclude: (I) a stream of C4 and lighter hydrocarbons passing throughline 40, (2) a light naphtha side stream passing through line 42, (3) aheavy naphtha side stream recovered as a product through line 44 orrecycled to the fresh naphtha feed line through line 12, (4) a light gasoil side stream passing through line 46, (5) an intermediate gas oilrecovered through line 30 as a cycle gas oil stream and recycled as feedto the catalytic cracking unit, and (6) a heavy gas oil bottoms productrecovered through line 43.

Catalyst is withdrawn from the bottom of the reactor through slidevalves 50 and 52 passing into stripping zone 54 containing baffles 56.Steam is introduced into the lower portion of stripper 54 to removeadsorbed and entrained hydrocarbons from the catalyst as it passesthrough the stripper. Stripped catalyst is withdrawn from the bottom ofthe stripping zone through spent catalyst standpipe 5S and dischargesinto regen erator 60. The catalyst forms a dense bed within regenerator160 and is regenerated therein by contacting it with air to remove thecarbon from the catalyst surface. Regenerated catalyst is withdrawn fromthe bottom of regenerator 60 through standpipes 16, 28 and 34 to supplythe hot regenerated catalyst to risers 14, 26 and 32, respectively, ashereinbefore described.

The process described above and illustrated in FIG. 1 may be conductedin the apparatus depicted in FIG. 2. Referring to FIG. 2, those itemsidentified by numbers with prime notations designate correspondingportions of the equipment illustrated in FIG. 1 by the same numbers butwithout the prime notation. Additional numbers are employed in FIG. 2 todesignate portions of the apparatus not illustrated or detailed in FIG.1.

The charge stocks, fresh naphtha and recycle naphtha, cycle gas oil andfresh gas oil in lines 10', 30' and 24, respectively, are introducedinto risers 14', 32 and 26', respectively, where they are contacted withzeolite cracking catalyst from standpipes 16', 34 and 28', respectively.The mixtures of oil and catalyst pass through their respective risersdischarging into reactor 18' where risers 26' and 32 terminate indownwardly directed outlets 19. The serrated edge provides smooth flowof the effluent from the risers, particularly when the dense bed level21 fluctuates near the downwardly projecting portion of the riser. Theeffluents passing from risers l4 and 32' pass upwardly through the densephase bed in reactor 18' effecting further conversion of the cycle gasoil and naphtha streams. The vaporous effluent from riser 26 dischargesinto vapor space 22' (also known as the dilute phase of catalyst). Thoseskilled in the art will readily appreciate that by varying level 21 ofthe dense phase of catalyst numerous combinations of riser cracking andbed cracking may be obtained for the feedstocks passing through risers26 and 32'. Thus, with the dense bed level 21 covering the outlets ofboth risers 26 and 32', the cycle gas oil and fresh gas oil will beriser cracked and bed cracked. With the catalyst level as indicated inFIG. 2,

the fresh gas oil will be only riser cracked while the cycle gas oilwill be riser cracked and bed cracked. Dropping the level below theoutlet of riser 32 results in the cycle gas oil and fresh gas oil onlybeing riser cracked. In all these situations the naphtha stream would besubjected to both riser and bed cracking.

Particles of catalyst in vapors passing through the dilute phase ofcatalyst 22' disengage from the vapors and fall back into the dense bedof catalyst. The vapors and entrained catalyst pass through cyclone 35where the entrained catalyst is separated and returned to dense bedthrough dip leg 37 and valve 39. A single cyclone has been shown forclarity but it will be understood that several cyclones may be assembledin series to achieve the desired separation. Effluent gases pass fromcyclone 35 into plenum chamber 41 from where the gases are dischargedfrom the reactor through line 43 to product recovery, not shown, wherethe conversion products are recovered and separated into desiredproducts and recycle streams, usually by distillation facilities wellknown in the art.

Steam introduced to steam ring 45 in the lower portion of the reactorstrips the catalyst as it passes downwardly through the bottom portionof the reactor through slide valves 50' and 52' into stripping chamber54'. Stripping chamber 54' is provided with baffles 56' attached to thewall of stripper 54]" and riser 14'. As the catalyst cascades down overthe baffles steam introduced through steam rings 53 and 55 displaces andremoves adsorbed and entrained hydrocarbon vapors which pass upwardlythrough the stripper venting through stripper vent line 57 and.discharge into vapor space 22 of reactor 18'.

Stripped catalyst is withdrawn from the bottom of stripping chamber 54passing through line 58' and discharges into regenerator 60. Airintroduced through air ring 62 at the bottom of regenerator 60 burns thecarbon from the surface of the catalyst in dense bed 64. The resultingflue gas passes upwardly entering cyclone where entrained catalyst isseparated and returned to catalyst bed 64 through dip leg 72. Flue gaspasses from the cyclone into plenum chamber 74 and through flue gas line76 to vent facilities. Regenerated catalyst is withdrawn from the bottomof the regenerator at rates controlled by slide valves 80, 82 and 84 tosupply hot regenerated catalyst to standpipes 28, 34' and 16',respectively, as described above.

The following exemplifies the practice of our invention and itsadvantages over alternative or prior art processes. A series of fourruns are performed with a fluidized catalytic cracking unit having twofeed risers. The same zeolite-containing cracking catalyst is employedin all runs. The catalyst consists of a 1:1 weight blend of a zeolitecracking catalyst and a high alumina amorphous cracking catalyst. Thezeolite catalyst comprises 18 weight percent of a type X zeolite in asilicaalumina matrix and has a rare earth content of about 2.9 weightpercent. The amorphous silica-alumina catalyst has a high aluminacontent, a surface area of about m /g, and a pore volume of about 0.44cc/g. in each of the runs fresh naphtha and fresh gas oil serve as thefeedstocks. The properties of the naphtha, a heavy straight rungasoline, are set forth in Table I while those of the gas oil arepresented in Table II.

TABLE I Feedstock Analysis Heavy Straight TABLE l-Continued FeedstockAnalysis Heavy Straight By comparing Run 1 with Run 2 it is seen thatsegregated cracking, i.e., cracking of naphtha and gas oil in separaterisers, produces a significant improvement in the octane of the productnaphtha obtained without a Description Run Gasohne 5 loss in totalnaphtha (DB naphtha plus alkylate) pro- R i Z 13 8 duction. Further,recycling heavy naphtha causes a sig- Paraffins 48:3 nificant increasein the octane number of the naphtha. Naphlhenes This is seen bycomparing Run 1 with Run 3 (92.6 to (1) Octane rating with addition of3cc tetraethyllead 10 Run 2 wlth Run 4 to per gallon Comparing Runs 3 and4 shows that by employing both naphtha recycle and segregated cracking ahigher TABLE H yield of a given octane uality naphtha can be obtamed. inaddition, coke yield and the amount of naph- Feedswck Analysis tharecycled are significantly lower in Run 4 than in Description Ga on Run3. Runs 2 and 4, illustrating our invention, clearly Gravity OAP 3O 9show the advantage of these improvements.

o Weclaim: 10 lli Distillation F' 403 l. A process for the catalyticcracking of naphtha and Ag 0 gas oil with a zeolite cracking catalyst ina fluid cata- 50 632 lytic cracking unit comprising a reactor, aregenerator 2% gig and a multiplicity of elongated reaction zoneswherein said reactor contains a dense phase and a dilute phaseAtmospheric equivalent temperatures of said catalyst and said elongatedreaction zones terminate at said reactor which comprises: ht Ruhs 1 and3 the gas oil and naphtha are combined W a. introducing a low octanefresh naphtha stream and in a ratio of 3:1 and introduced into a singleriser. Both a fi portion of a freshly regenerated li R5 ??[Qhlhgg gtgtit emperatyrcgf 291553 351 cracking catalyst into a first elongatedreaction and 3 are the same in all respects except that in Run 3, zoneto form a first mixture consisting essentially of a heavy naphthafraction is recovered from the reactor said f h naphtha Stream and Saidfirst portion f effluent and recycled to the feed riser. In Runs 2 andcatalyst, demonstrating the process of our invention the gas b. passingreactants consisting essentially of said first oil and naphtha aresegregated and introduced into sepmixture through said first elongatedreaction Zone arate risers. Again, both runs are made with risertemunder naphtha cracking Conditions, F P 9 920? h effluent fmm,thenaphtha 3 5 c. introducing a virgin gas oil stream and a second riser issub ected to additional bed cracking at 920F. portion of freshlyregenemted Zeome cracking increased conversion of h naphtha-1 Run 2alyst into a second elongated reaction zone to form employs no.naphtharecycle but m Run 4 a heavy a second mixture consisting essentially ofsaid virnaphtha cut 15 taken from the reactor effluent and recygin gason Stream and said second onion of Cata cled to the naphtha riser. y p

Operating data and results of these runs are presd assin react m n f p lfiqg .r gmlgd z g M M u p 7 g a s COllSlS mg essen ia y 0 sm sec TABLEill Run No. 1 Total Fresh Feed Composition :25 wt. Blend Gas Oil 8LNaphtha 75:25 wt. Blend Gas Oil & Naphtha 75:25 wt. Blend Gas Oil &Naphtha 3 75:25 wt. Blend Gas Oil & Naphtha Gas Oil Gas Oil 84 NaphthaGas Oil Naphtha Naphtha Notes: 1. Net yield. Does not include materialconsumed in producing alkylate. 2. Dehutnnized naphtha.

3. RON 3 cc TEL Research Octane Number with addition otzlicctetraethylle d per gallon nd mixture through said second elongatedreaction zone under gas oil cracking conditions.

e. discharging the effluents from said first and second reaction zonesinto a catalyst phase in said reactor, said effluents comprisingvaporous reaction mixture and catalyst, and

. recovering from the vaporous reaction mixture in a dilute phase ofcatalyst in said reactor a fraction boiling in the range of 100 to 450F.having an octane rating higher than said fresh naphtha stream and afraction boiling below 100F.

2. A process according to claim 1 wherein the naphtha crackingconditions of step (a) include a temperature of 750-l,300F., aconversion of 25-80 volume percent and a vapor velocity of 15-50feet/second and the gas oil cracking conditions of step (b) include atemperature of 840-l,l00F., a conversion of 30-80 volume percent and avapor velocity of 15-50 feet/- second.

3. A process according to claim 2 wherein the effluents from the firstand second elongated reaction zones are discharged into a dilute phaseof catalyst.

4. A process according to claim 2 wherein the effluent from the firstelongated reaction zone is discharged into a dilute phase of catalystand the effluent from the second elongated reaction zone is dischargedinto a dense phase of catalyst, said vaporous reaction mixture from saidsecond elongated reaction zone passing through said dense phase undercatalytic cracking conditions effecting an additional conversion of 5-50volume percent and discharging into a dilute phase of catalyst.

5. A process according to claim 2 wherein the effluent from the secondelongated reaction zone is discharged into a dilute phase of catalystand the effluent from the first elongated reaction zone is dischargedinto a dense phase of catalyst, said vaporous reaction mixture from saidfirst elongated reaction zone passing through said dense phase undercatalytic cracking conditions effecting an additional conversion of 5-30volume percent and discharging into a dilute phase of catalyst.

6. A process according to claim 2 wherein the effluents from the firstand second elongated reaction zones are discharged into a dense phase ofcatalyst, said vaporous reaction mixtures from said first and secondreaction zones passing through said dense phase under catalytic crackingconditions effecting an additional conversion of 5-30 volume percent anddischarging into a dilute phase of catalyst.

7. A process according to claim 3 including the following additionalsteps:

g. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling above about500F.,

h. introducing the fraction from step (g) and a third portion offreshly-regenerated zeolite cracking catalyst into a third elongatedreaction zone to form a third mixture consisting essentially of saidfraction from step (g) and said third portion of catalyst,

i. passing reactants consisting essentially of third mixture throughsaid third elongated reaction zone under cycle gas oil crackingconditions, and

j. discharging the effluent from said third elongated reaction zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions effecting an additional conversionof 5-30 volume percent and discharging into a dilute phase of catalyst.

8. A process according to claim 4 including the following additionalsteps:

g. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling above about500F.,

h. introducing the fraction from step (g) and a third portion offreshly-regenerated zeolite cracking catalyst into a third elongatedreaction zone to form a third mixture consisting essentially of saidfraction from step (g) and said third portion of catalyst,

i. passing reactants consisting essentially of said third mixturethrough said third elongated reaction zone under cycle gas oil crackingconditions, and

j. discharging the effluent from said third elongated reaction zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions effecting an additional conversionof 5-30 volume percent and discharging into a dilute phase of catalyst.

9. A process according to claim 5 including the following additionalsteps:

g. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling above about500F.,

h. introducing the fraction from step (g) and a third portion offreshly-regenerated zeolite cracking catalyst into a third elongatedreaction zone to form a third mixture consisting essentially of saidfraction from step (g) and said third portion of catalyst,

i. passing reactants consisting essentially of said third mixturethrough said third elongated reaction zone under cycle gas oil crackingconditions, and

j. discharging the effluent from said third elongated reaction zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions effecting an additional conversionof 5-30 volume percent and discharging into a dilute P s q s telv 10. Aprocess according to claim 6 including the following additional steps:

j. discharging the effluent from said third elongated reaction Zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions effecting an additional conversionof -30 volume percent and discharging into a dilute phase of catalyst.

1 l. A process according to claim 4 wherein the catalytic crackingconditions in the dense phase include a temperature of 800-1,150F. and avapor velocity of 0.5-4 feet/second.

12. A process according to claim 5 wherein the catalytic crackingconditions in the dense phase include a temperature of 800-l,l50F. and avapor velocity of 0.5-4 feet/second.

13. A process according to claim 6 wherein the catalytic crackingconditions in the dense phase include a temperature of 800-1,l50F. and avapor velocity of 0.5-4 feet/second.

14. A process according to claim 7 wherein the cycle gas oil crackingconditions of step (f) include a temperature of 800-1 ,100F., aconversion of 20-70 volume percent and a vapor velocity of 15-50feet/second and the catalytic cracking conditions in the dense phaseinclude a temperature of 800-1,l50F. and a vapor velocity of 0.5-4feet/second.

15. A process according to claim 8 wherein the cycle gas oil crackingconditions of step (f) include a temperature of 800-l,100F., aconversion of 20-70 volume percent and a vapor velocity of 15-50feet/second and the catalytic cracking conditions in the dense phaseinclude a temperature of 800-l,l50F. and a vapor velocity of 0.5-4feet/second.

16. A process according to claim 9 wherein the cycle gas oil crackingconditions of step (f) include a temperature of 800-l,100F., aconversion of 20-70 volume percent and a vapor velocity of 15-50feet/second and the catalytic cracking conditions in the dense phaseinclude a temperature of 800-1,150F. and a vapor velocity of 0.5-4feet/second.

17. A process according to claim 10 wherein the cycle gas oil crackingconditions of step (f) include a temperature of 800l,l00F., a conversionof 20-70 volume percent and a vapor velocity of :50 feet/- second andthe catalytic cracking conditions in the dense phase include atemperature of 800-l,150F. and a vapor velocity of 0.5-4 feet/second.

18. A process for the catalytic cracking of naphtha and gas oil with azeolite cracking catalyst in a fluid catalytic cracking unit comprisinga reactor, a regenerator and a multiplicity of elongated reaction zoneswherein said reactor contains a dense phase and a dilute phase of saidcatalyst and said elongated reaction zones terminate at said reactorwhich comprises:

a. introducing a low octane fresh naphtha stream, the hydrocarbonfraction boiling above aboutt 592? of step (h) herein and a firstportion of a freshlyregenerated zeolite cracking catalyst into a firstelongated reaction zone to form a fourth mixture consisting essentiallyof said fresh naphtha stream, said fraction boiling above abogt 500F.and said I first portion of catalyst,

b. passing reactants consisting essentially of said fourth mixturethrough said first elongated reaction zone under naphtha crackingconditions,

c. discharging the effluent from said first elongated reaction zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst,

cl. passing said vaporous reaction mixture from step (c) through saiddense phase under catalyst cracking conditions and discharging into adilute phase of catalyst,

e. introducing a virgin gas oil stream and a second portion offreshly-regenerated zeolite cracking catalyst into a second elongatedreaction zone to form a fifth mixture consisting essentially of saidvirgin gas oil stream and said second portion of catalyst,

f. passing reactants consisting essentially of said fifth mixturethrough said second elongated reaction zone under gas oil crackingconditions,

g. discharging the effluent from said second elongated reaction zoneinto a catalyst phase in said reactor, said effluent comprising vaporousreaction mixture and catalyst,

h. recovering from the vaporous reaction mixture in a dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling above about500F., and

i. recovering as products from the vaporous reaction mixture in a dilutephase of catalyst in said reactor a fraction boiling in the range of to450F. having an octane rating higher than said fresh naphtha stream anda fraction boiling below 100F.

19. A process according to claim 18 wherein the naphtha crackingconditions of step (b) include a temperature of 750-l,300F., aconversion of 25-80 volume percent and a vapor velocity of l5-50ft/sec., the gas oil cracking conditions of step (f) include atemperature of 840-1,100F., a conversion of 30-80 volume percent and avapor velocity of 15-50 ft/sec. and the catalytic cracking conditions inthe dense phase in clude a temperature of 800-l ,150F., a vapor velocityof 0.5-4 ft/sec. and an additional conversion of 5-30 XQlHFPEPi EFHP .7

20. A process according to claim 19 wherein the effluent from the secondelongated reaction zone is disrhsr d. i 99 a di ate P e t t l st:

21. A process according to claim 18 wherein the effluent from the secondelongated reaction zone is discharged into a dense phase of catalyst,said vaporous reaction mixture from said second elongated reaction zonepassing through said dense phase under catalytic cracking conditions anddischarging into a dilute phase 9 c taly 22. A process for the catalyticcracking of naphtha and gas oil with a zeolite cracking catalyst in afluid catalytic cracking unit comprising a reactor, a regenerator and amultiplicity of elongated reaction zones wherein said reactor contains adense phase and a dilute phase of said catalyst and said elongatedreaction zones terminate at said reactor which comprises:

a. introducing a low octane fresh naphtha stream, the hydrocarbonfraction boiling between 100 and 450Fsfrom step (h) herein and a firstportion of fresiily regenerated zeoli te cracking catalyst into a firstelongated reaction zone to form a sixth mixture consisting essentiallyof said fresh naphtha stream, said fraction boiling between 100 and 450}and said first portion of catalyst,

1 b passing reactants consisting essentially of said sixth mixturethrough said first elongated reaction zone under naphtha crackingconditions,

c. discharging the effluent from said first elongated reaction zone intoa dense phase of said catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst,

d. passing said vaporous reaction mixture from step (c) through saiddense phase under catalytic cracking conditions and discharging into adilute phase of catalyst,

e. introducing a virgin gas oil and a second portion offreshly-regenerated zeolite cracking catalyst into a second elongatedreaction zone to form a seventh mixture consisting essentially of saidvirgin gas oil and said second portion of catalyst,

f. passing reactants consisting essentially of said seventh mixturethrough said second elongated reaction zone under gas oil crackingconditions,

g. discharging the effluent from said second elongated reaction zoneinto a catalyst phase in said reactor, said effluent comprising vaporousreaction mixture and catalyst,

h. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor 21 hydrocarbon fraction boiling between 100 and450F, and

i. recovering as products from the vaporous reaction mixture in thedilute phase of catalyst in said reactor a fraction boiling in the rangeof 100 to 450F. having an octane rating higher than said fresh naphthastream and a fraction boiling below 100F.

23. A process according to claim 22 wherein the naphtha crackingcondtions of step (b) include a temperature of 750-l,300F., a conversionof 25-80 voume percent and a vapor velocity of l550 ft/sec., the gas oilcracking conditions of step (f) include a temperature of 840 l,llF., aconversion of 30-80 volume percent and a vapor velocity of l-50 ft/sec.and the catalytic cracking conditions in the dense phase include atemperature of 800-l,l50F., a vapor velocity of 0.5-4 ft/sec. and anadditional conversion of 5-30 volume percent.

24. A process according to claim 23 wherein the effluent from the secondelongated reaction zone is discharged into a dilute phase of catalyst. h

25. A process according to claim 23 wherein the effluent from the secondelongated reaction zone is discharged into a dense of catalyst, saidvaporous reaction mixture from said second elongated reaction zonepassing through said dense phase under catalytic cracking conditions anddischarging into a dilute phase of catalyst.

26. A process according to claim 24 including t he following additionalsteps:

j. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in :said reactor a hydrocarbon fraction boiling above 500F.,

k. introducing said fraction of step (j) and a third portion offreshly-regenerated zeolite cracking catalyst into a third elongatedreaction zone to form an eighth mixture consisting essentially of saidfraction from step (j) and said third portion of catalyst,

l. passing reactants consisting; essentially of said eighth mixturethrough said elongated reaction zone under cycle gas oil crackingconditions, and

m. discharging the effluent from said third elongated reaction zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions and discharging into a dilute phaseof catalyst.

27. A process according to claim 25 including the following additionalsteps: is

j. recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling above 500F.,

k. introducing said fraction of step (j) and a third portion offreshly-regenerated zeolite cracking catalyst into a third elongatedreaction zone to form an eighth mixture consisting essentially of saidfraction from step (j) and said third portion of catalyst,

l. passing reactants consisting essentially of said eighth mixturethrough said elongated reaction zone under cycle gas oil crackingconditions, and

m. discharging the effluent from said third elongated reaction zone intoa dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongate-d reaction zone passing through said densephase under catalytic cracking conditions and discharging into a dilutephase of catalyst.

28. A process according to claim 26 wherein the cycle gas oil crackingconditions of step (1) include a temperature of 800-l,l0OF., aconversion of 20-70 volume percent and a vapor velocity of 15-50 ft/sec.

29. A process according to claim 27 wherein the cycle gas oil crackingconditions of step (1) include a temperature of 800l,l00F., a conversionof 2070 volume percent and a vaponvelocity of 15-50 ft/sec.

2. A process according to claim 1 wherein the naphtha crackingconditions of step (a) include a temperature of 750*-1,300*F., aconversion of 25-80 volume percent and a vapor velocity of 15-50feet/second and the gas oil cracking conditions of step (b) include atemperature of 840*-1,100*F., a conversion of 30-80 volume percent and avapor velocity of 15-50 feet/second.
 3. A process according to claim 2wherein the effluents from the first and second elongated reaction zonesare discharged into a dilute phase of catalyst.
 4. A process accordingto claim 2 wherein the effluent from the first elongated reaction zoneis discharged into a dilute phase of catalyst and the effluent from thesecond elongated reaction zone is discharged into a dense phase ofcatalyst, said vaporous reaction mixture from said second elongatedreaction zone passing through said dense phase under catalytic crackingconditions effecting an additional conversion of 5-50 volume percent anddischarging into a dilute phase of catalyst.
 5. A process according toclaim 2 wherein the effluent from the second elongated reaction zone isdischarged into a dilute phase of catalyst and the effluent from thefirst elongated reaction zone is discharged into a dense phase ofcatalyst, said vaporous reaction mixture from said first elongatedreaction zone passing through said dense phase under catalytic crackingconditions effecting an additional conversion of 5-30 volume percent anddischarging into a dilute phase of catalyst.
 6. A process according toclaim 2 wherein the effluents from the first and second elongatedreaction zones are discharged into a dense phase of catalyst, saidvaporous reaction mixtures from said first and second reaction zonespassing through said dense phase under catalytic cracking conditionseffecting an additional conversion of 5-30 volume percent anddischarging into a dilute phase of catalyst.
 7. A process according toclaim 3 including the following additional steps: g. recovering from thevaporous reaction mixture in the dilute phase of catalyst in saidreactor a hydrocarbon fraction boiling above about 500*F., h.introducing the fraction from step (g) and a third portion offreshly-regenerated zeolite cracking catalyst into a third elongatedreaction zone to form a third mixture consisting essentially of saidfraction from step (g) and said third portion of catalyst, i. passingreactants consisting essentially of third mixture through said thirdelongated reaction zone under cycle gas oil cracking conditions, and j.discharging the effluent from said third elongated reaction zone into adense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions effecting an additional conversionof 5-30 volume percent and discharging into a dilute phase of catalyst.8. A process according to claim 4 including the following additionalsteps: g. recovering from the vaporous reaction mixture in the dilutephase of catalyst in said reactor a hydrocarbon fraction boiling aboveabout 500*F., h. introducing the fraction from step (g) and a thirdportion of freshly-regenerated zeolite cracking catalyst into a thirdelongated reaction zone to form a third mixture consisting essentiallyof said fraction from step (g) and said third portion of catalyst, i.passing reactants consisting essentially of said third mixture throughsaid third elongated reaction zone under cycle gas oil crackingconditions, and j. discharging the effluent from said third elongatedreaction zone into a dense phase of catalyst in said reactor, saideffluent comprising vaporous reaction mixture and catalyst, saidvaporous reaction mixture from said third elongated reaction zonepassing through said dense phase under catalytic cracking conditionseffecting an additional conversion of 5-30 volume percent anddischarging into a dilute phase of catalyst.
 9. A process according toclaim 5 including the following additional steps: g. recovering from thevaporous reaction mixture in the dilute phase of catalyst in saidreactor a hydrocarbon fraction boiling above about 500*F., h.introducing the fraction from step (g) and a third portion offreshly-regenerated zeolite cracking catalyst into a third elongatedreaction zone to form a third mixture consisting essentially of saidfraction from step (g) and said third portion of catalyst, i. passingreactants consisting essentially of said third mixture through saidthird elongated reaction zone under cycle gas oil cracking conditions,and j. discharging the effluent from said third elongated reaction zoneinto a dense phase of catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, said vaporous reaction mixturefrom said third elongated reaction zone passing through said dense phaseunder catalytic cracking conditions effecting an additional conversionof 5-30 volume percent and discharging into a dilute phase of catalyst.10. A process according to claim 6 including the following additionalsteps: g. recovering from the vaporous reaction mixture in the dilutephase of catalyst in said reactor a hydrocarbon fraction boiling aboveabout 500*F., h. introducing the fraction from step (g) and a thirdportion of freshly-regenerated zeolite cracking catalyst into a thirdelongated reaction zone to form a third mixtuRe consisting essentiallyof said fraction from step (g) and said third portion of catalyst, i.passing reactants consisting essentially of said third mixture throughsaid third elongated reaction zone under cycle gas oil crackingconditions, and j. discharging the effluent from said third elongatedreaction zone into a dense phase of catalyst in said reactor, saideffluent comprising vaporous reaction mixture and catalyst, saidvaporous reaction mixture from said third elongated reaction zonepassing through said dense phase under catalytic cracking conditionseffecting an additional conversion of 5-30 volume percent anddischarging into a dilute phase of catalyst.
 11. A process according toclaim 4 wherein the catalytic cracking conditions in the dense phaseinclude a temperature of 800*-1,150*F. and a vapor velocity of 0.5-4feet/second.
 12. A process according to claim 5 wherein the catalyticcracking conditions in the dense phase include a temperature of800*-1,150*F. and a vapor velocity of 0.5-4 feet/second.
 13. A processaccording to claim 6 wherein the catalytic cracking conditions in thedense phase include a temperature of 800*-1,150*F. and a vapor velocityof 0.5-4 feet/second.
 14. A process according to claim 7 wherein thecycle gas oil cracking conditions of step (f) include a temperature of800*-1, 100*F., a conversion of 20-70 volume percent and a vaporvelocity of 15-50 feet/second and the catalytic cracking conditions inthe dense phase include a temperature of 800*-1,150*F. and a vaporvelocity of 0.5-4 feet/second.
 15. A process according to claim 8wherein the cycle gas oil cracking conditions of step (f) include atemperature of 800*-1, 100*F., a conversion of 20-70 volume percent anda vapor velocity of 15-50 feet/second and the catalytic crackingconditions in the dense phase include a temperature of 800*-1,150*F. anda vapor velocity of 0.5-4 feet/second.
 16. A process according to claim9 wherein the cycle gas oil cracking conditions of step (f) include atemperature of 800*-1, 100*F., a conversion of 20-70 volume percent anda vapor velocity of 15-50 feet/second and the catalytic crackingconditions in the dense phase include a temperature of 800*-1,150*F. anda vapor velocity of 0.5-4 feet/second.
 17. A process according to claim10 wherein the cycle gas oil cracking conditions of step (f) include atemperature of 800*-1, 100*F., a conversion of 20-70 volume percent anda vapor velocity of 15-50 feet/second and the catalytic crackingconditions in the dense phase include a temperature of 800*-1,150*F. anda vapor velocity of 0.5-4 feet/second.
 18. A process for the catalyticcracking of naphtha and gas oil with a zeolite cracking catalyst in afluid catalytic cracking unit comprising a reactor, a regenerator and amultiplicity of elongated reaction zones wherein said reactor contains adense phase and a dilute phase of said catalyst and said elongatedreaction zones terminate at said reactor which comprises: a. introducinga low octane fresh naphtha stream, the hydrocarbon fraction boilingabove about 500*F. of step (h) herein and a first portion of afreshly-regenerated zeolite cracking catalyst into a first elongatedreaction zone to form a fourth mixture consisting essentially of saidfresh naphtha stream, said fraction boiling above about 500*F. and saidfirst portion of catalyst, b. passing reactants consisting essentiallyof said fourth mixture through said first elongated reaction zone undernaphtha cracking conditions, c. discharging the effluent from said firstelongated reaction zone into a dense phase of catalyst in said reactor,said effluent comprising vaporous reaction mixture and catalyst, d.passing said vaporous reaction mixture from step (c) through said densephase under catalyst cracking conditions and discharging into a dilutephase of catalyst, e. introducing a virgin gas oil stream and a secondportion of freshly-regenerated zeolite cracking catalyst into a secondelongated reaction zone to form a fifth mixture consisting essentiallyof said virgin gas oil stream and said second portion of catalyst, f.passing reactants consisting essentially of said fifth mixture throughsaid second elongated reaction zone under gas oil cracking conditions,g. discharging the effluent from said second elongated reaction zoneinto a catalyst phase in said reactor, said effluent comprising vaporousreaction mixture and catalyst, h. recovering from the vaporous reactionmixture in a dilute phase of catalyst in said reactor a hydrocarbonfraction boiling above about 500*F., and i. recovering as products fromthe vaporous reaction mixture in a dilute phase of catalyst in saidreactor a fraction boiling in the range of 100* to 450*F. having anoctane rating higher than said fresh naphtha stream and a fractionboiling below 100*F.
 19. A process according to claim 18 wherein thenaphtha cracking conditions of step (b) include a temperature of750*-1,300*F., a conversion of 25-80 volume percent and a vapor velocityof 15-50 ft/sec., the gas oil cracking conditions of step (f) include atemperature of 840*-1,100*F., a conversion of 30-80 volume percent and avapor velocity of 15-50 ft/sec. and the catalytic cracking conditions inthe dense phase include a temperature of 800*-1,150*F., a vapor velocityof 0.5-4 ft/sec. and an additional conversion of 5-30 volume percent.20. A process according to claim 19 wherein the effluent from the secondelongated reaction zone is discharged into a dilute phase of catalyst.21. A process according to claim 18 wherein the effluent from the secondelongated reaction zone is discharged into a dense phase of catalyst,said vaporous reaction mixture from said second elongated reaction zonepassing through said dense phase under catalytic cracking conditions anddischarging into a dilute phase of catalyst.
 22. A process for thecatalytic cracking of naphtha and gas oil with a zeolite crackingcatalyst in a fluid catalytic cracking unit comprising a reactor, aregenerator and a multiplicity of elongated reaction zones wherein saidreactor contains a dense phase and a dilute phase of said catalyst andsaid elongated reaction zones terminate at said reactor which comprises:a. introducing a low octane fresh naphtha stream, the hydrocarbonfraction boiling between 100 and 450*F from step (h) herein and a firstportion of freshly-regenerated zeolite cracking catalyst into a firstelongated reaction zone to form a sixth mixture consisting essentiallyof said fresh naphtha stream, said fraction boiling between 100 and450*F and said first portion of catalyst, b. passing reactantsconsisting essentially of said sixth mixture through said firstelongated reaction zone under naphtha cracking conditions, c.discharging the effluent from said first elongated reaction zone into adense phase of said catalyst in said reactor, said effluent comprisingvaporous reaction mixture and catalyst, d. passing said vaporousreaction mixture from step (c) through said dense phase under catalyticcracking conditions and discharging into a dilute phase of catalyst, e.introducing a virgin gas oil and a second portion of freshly-regeneratedzeolite cracking catalyst into a second elongated reaction zone to forma seventh mixture consisting essentially of said virgin gas oil and saidsecond portion of catalyst, f. passing reactants consisting essentiallyof said seventh mixture through said second elongated reaction zoNeunder gas oil cracking conditions, g. discharging the effluent from saidsecond elongated reaction zone into a catalyst phase in said reactor,said effluent comprising vaporous reaction mixture and catalyst, h.recovering from the vaporous reaction mixture in the dilute phase ofcatalyst in said reactor a hydrocarbon fraction boiling between 100* and450*F, and i. recovering as products from the vaporous reaction mixturein the dilute phase of catalyst in said reactor a fraction boiling inthe range of 100* to 450*F. having an octane rating higher than saidfresh naphtha stream and a fraction boiling below 100*F.
 23. A processaccording to claim 22 wherein the naphtha cracking condtions of step (b)include a temperature of 750*-1,300*F., a conversion of 25-80 voumepercent and a vapor velocity of 15-50 ft/sec., the gas oil crackingconditions of step (f) include a temperature of 840*-1,100*F., aconversion of 30-80 volume percent and a vapor velocity of 15-50 ft/sec.and the catalytic cracking conditions in the dense phase include atemperature of 800*-1,150*F., a vapor velocity of 0.5-4 ft/sec. and anadditional conversion of 5-30 volume percent.
 24. A process according toclaim 23 wherein the effluent from the second elongated reaction zone isdischarged into a dilute phase of catalyst.
 25. A process according toclaim 23 wherein the effluent from the second elongated reaction zone isdischarged into a dense of catalyst, said vaporous reaction mixture fromsaid second elongated reaction zone passing through said dense phaseunder catalytic cracking conditions and discharging into a dilute phaseof catalyst.
 26. A process according to claim 24 including the followingadditional steps: j. recovering from the vaporous reaction mixture inthe dilute phase of catalyst in said reactor a hydrocarbon fractionboiling above 500*F., k. introducing said fraction of step (j) and athird portion of freshly-regenerated zeolite cracking catalyst into athird elongated reaction zone to form an eighth mixture consistingessentially of said fraction from step (j) and said third portion ofcatalyst, l. passing reactants consisting essentially of said eighthmixture through said elongated reaction zone under cycle gas oilcracking conditions, and m. discharging the effluent from said thirdelongated reaction zone into a dense phase of catalyst in said reactor,said effluent comprising vaporous reaction mixture and catalyst, saidvaporous reaction mixture from said third elongated reaction zonepassing through said dense phase under catalytic cracking conditions anddischarging into a dilute phase of catalyst.
 27. A process according toclaim 25 including the following additional steps: j. recovering fromthe vaporous reaction mixture in the dilute phase of catalyst in saidreactor a hydrocarbon fraction boiling above 500*F., k. introducing saidfraction of step (j) and a third portion of freshly-regenerated zeolitecracking catalyst into a third elongated reaction zone to form an eighthmixture consisting essentially of said fraction from step (j) and saidthird portion of catalyst, l. passing reactants consisting essentiallyof said eighth mixture through said elongated reaction zone under cyclegas oil cracking conditions, and m. discharging the effluent from saidthird elongated reaction zone into a dense phase of catalyst in saidreactor, said effluent comprising vaporous reaction mixture andcatalyst, said vaporous reaction mixture from said third elongatedreaction zone passing through said dense phase under catalytic crackingconditions and discharging into a dilute phase of catalyst.
 28. Aprocess according to claim 26 wherein the cycle gas oil crackingconditions of step (1) include a temperature of 800*-1, 100*F., aconverSion of 20-70 volume percent and a vapor velocity of 15-50 ft/sec.29. A process according to claim 27 wherein the cycle gas oil crackingconditions of step (1) include a temperature of 800*-1, 100*F., aconversion of 20-70 volume percent and a vapor velocity of 15-50 ft/sec.